A low-friction seal of this type is known from EP 0043 918 B1. This low-friction seal is realized in the form of a so-called contactless seal, i.e., a nearly frictionless seal, in which the sealing effect is realized by means of a sealing gap between the sealing ring and the location to be sealed. The viscous effect of the fluid situated in this sealing gap ensures an appropriate seal. Due to the contactless arrangement, this seal is, in contrast to conventional seals, theoretically frictionless. However, a residual friction which results from the adhesion of the fluid actually exists. For this reason, the following description refers to “low-friction” seals.
The previously mentioned known seal contains a dimensionally stable sealing ring that is accommodated with axial and radial clearance in a groove of one of two surfaces that need to be sealed relative to one another and move relative to one another. The periphery of the sealing ring which protrudes from the groove is arranged opposite to the other surface to be sealed, namely with a sliding fit. In this known seal, spacer means which allow an unobstructed propagation of pressure to the bottom of the groove are also provided between the sidewall of the groove on the side of the pressure chamber and the sealing ring, with the cylindrical surface of the sealing ring which protrudes from the groove adjoining the other surface to be sealed with a sliding fit and containing a series of small annular grooves arranged at longitudinal distances to one another. In order to supplement the sealing function of a sealing edge that acts upon the sidewall of the groove which is situated distant from the pressure chamber, an elastic sealing ring is arranged within the region of the sealing edge. In this known seal, the pressure medium is able to flow from the pressure chamber to the bottom of the groove between the spacers while attempting to escape past the sealing edge. However, the pressure medium is prevented from doing so because the sealing ring has a larger surface which is charged with pressure on the side of the spacers than on the side opposite the sealing edge, i.e., the sealing ring is held such that it adjoins the sealing edge by the pressure that propagates within the groove in an unobstructed fashion. This means that the sealing ring is essentially held in a floating fashion within the groove that is charged with the pressure medium. In order to achieve a reduced friction, this known seal does not fulfill any guide functions. Since the pressure medium that is propagated in the narrow gap between the surface to be sealed, e.g., a piston rod, and the periphery of the sealing ring attempts to escape from the pressure chamber past the sealing ring, hydrodynamic forces are created which cause the pressure medium to distribute around the piston rod in a largely uniform fashion and to preserve a concentric gap. The clearance between the sealing ring and the groove is so large that the pressure from the oil chamber is able to propagate to the bottom of the groove in an unobstructed fashion as long as said pressure continues through the slideway gap between the guide bushing and the piston rod. This known arrangement aims to reduce friction losses, in particular, pressure-dependent friction losses, between surfaces which move relative to one another in a translational fashion and to significantly increase the degree of efficiency.
Based on this state of the art, the invention aims to develop a seal of the initially mentioned type, in which a simplified design is achieved and the advantageous effects known from the state of the art are preserved. In addition, the pressures acting upon the sealing ring of the new seal should be realized such that materials with a greater expansion can also be used for the sealing ring.
According to the invention, this objective is achieved with a low-friction seal as set forth below.